i`m trying to help out a mate with his 2005 hummer h2 it starts and runs fine and drives lovely if you shift it manually but there is next to no power if you just put it in drive ! i have checked it with a dtc reader and got p0740 p0758 p0785 p2761 oh and p0753 as its been doing this for a little while and last week wiped out its gearbox its on a new box but codes and probs are the same is there a control module or is it controlled through the main confuser the speed sensor on the side of the box is from the old one could this be the prob sorry know little about auto boxes and can`t find help over here if anyone can advise it would be a great help even just for elimination purposes

Check the IGNO fuse in the fuse block lower left side of the dash. It's a 10amp fuse that supplies power to the transmission shift solenoids. Check for power at pin E (pink wire) in the transmission connector. There is also a pink wire in pin N which comes from the PCM. Pin E is the only wire in the transmission connector that does not come from, or go to the PCM. The codes you have all pertain to the shift solenoids and over drive, leading me to believe it is a power situation problem.

Let me know what you find, I hope this helps.

Certainly appears to be a communication problem to the tranny...

the trans will default to 3rd gear and the vehicle will drive like a slug in "OD or D"

Does the speed-O function?

Does the PRND321 indicator in the dash function?

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If you can't fix it with a hammer, you have an electrical problem.

the speedo does work as does the gear position indicator will check power on pink and let you know ! i`ve just taken all wrap off wiring to gearbox and there is no sign of damage
checked pink and voltage is present ign0 fuse is fine

I'll bet the PCM is bad, as, the PCM controls the shifting.

took the car to a superb garage in manchester ( 300 miles each way ) who found the fault in minutes turned out to be a not unknown fault with the ignition switch not powering up the gearbox ! even tho it had battery voltage with ignition on as soon as you started and drove it this faded out and hence nothing worked maybe this will help someone else in the future ! once again thanks for help and advice

Great news, now that it's fixed.

Often times when you have these types of codes and a problem with the ignition switch, you will have a problem with the speedometer operation.

This concern is checked at the fuse box, with a test light on the trans fuse or some other fuse, that excapes me right now.

Anyway, you wiggle the ignition switch while you watch the test light, if you lose power, during this test, the ignition switch is bad.